Gas purging of spinning packs

ABSTRACT

A process for improving the percentage of successful startups in spinning polymer from solution is provided. Startups are often hindered by the presence of air in the spinneret assembly. The present invention provides for replacing the air in the spinneret assembly with a gas more soluble than air in the solution to be spun.

United States Patent Berry, Jr- [4 1 June 20, 1972 54] GAS PURGING 0F SPINNING PACKS 3,458,6l6 7/1969 Guess et al ..264/204 3,461,193 8/1969 Gilardi ..264/53 [72] Inventor. t/vzflter Cunningham Berry, Jr., Staunton, 3.496.263 2,1970 Nakagama t aL mam/206 3,509,244 4/1970 Cochrane ..264 /205 I73] Assigncc: E. l. du Pont de Nemours and Company,

Wilmington Primary bZraminer-Jay H. W00 [22] Filed: Oct 19, 1970 Attorney-Martin R. Levy A process for improving the percentage of successful startups 52 us. Cl ..264/39, 264/85, 22664520615, in Spinning polymer from solution is provided Stamps are In CI B28.) 7/04 D01 f7 loo often hindered by the presence of air in the spinneret as- 58 1 Field 264/264 2O8 39 I 'sembly. The present invention provides for replacing the air in l 5 /3 45 the spinneret assembly with a gas more soluble than air in the solution to be spun.

[56] References Cited 4 Cl 1 Drawing Figure UNITED STATES PATENTS Mouchiroud et a1. "264/205 PATENTEDaunzo 1972 Q 3.671.653

r I?! l N ll l3 I5 I? I9 INVENTOR WALTER CUNNINGHAM BERRY. JR.

ATTORNEY GAS PURGING F SPINNING PACKS The present invention is concerned with spinning of synthetic filaments from solutions. Such solutions are typically forced through a spinneret assembly either into a spinning cell through which inert gas is circulated to evaporate solvent leaving a residual filament of the filament forming polymer (hereinafter called dry spinning); or, in the alternative, the solution is pumped through a spinneret assembly into a coagulating bath (hereinafter called wet spinning). In the coagulating bath the filamentary form of the filament forming polymer is established.

In either case, in starting up a spinning system in which solution of the fiber forming polymer in a solvent is forced through a spinneret assembly, there is an initial startup period during which spinning solution is first passed through the spinneret assembly. The assembly may or may not be preheated toequalize its temperature with that of the solution to be passed therethrough. However, typically the assembly contains air within its free volume. When the assembly containing air in its free volume is installed in the spinning cell, solution passing therethrough during startup forces some of the air directly ahead of it through the spinneret openings. Significant amounts of this air may be trapped and compressed within the assembly cavities. This air causes discontinuities in the spinning solution passing therethrough resulting in discontinuities in the filaments so prepared. Spinning solution may be deposited on the spinneret face. These interruptions and difficulties in startup may result in safety hazards and economic disadvantages.

The present invention provides a simple method of reducing the discontinuities in spinning startup as a result of air present in the free space of the spinneret assembly.

The present invention is a process which comprises replacing the air in the spinneret assembly with a gas more soluble than air in the solution to be spun. The spinneret assembly may be purged with such a gas (such as CO either before or after the spinneret assembly is connected to the outlet of the spinning cell (the outlet of the pumping system advancing the spinning solution). However, the purging of the spinneret assembly with the soluble gas" is carried out in any event before advancing solution therethrough.

The apparatus for purging the spinneret may comprise a commercial gas cylinder with a standard pressure regulator connected through tubing to the spinneret assembly. The tubing from the gas cylinder can be connected to the polymer inlets of the spinneret assembly and the purging gas can take the same path as the solution to be subsequently pumped therethrough. Alternatively, a manifold may be set up so that more than one assembly can be purged'simultaneously. The assembly should be installed as soon as conveniently possible after the replacement of the air with more soluble gas to prevent diffusion of air back into the spinneret assembly. Typical installation times should be less than minutes.

Grestest effectiveness of the process of the present invention is obtained if at startup the solution to be spun through the spinneret is at as low a temperature as convenient. It is postulated that this result is due to the increase in solubility of the soluble gas in the solution at lower temperatures.

DEFINITIONS Textile filaments are spun from solution by wet spinning" and dry spinning" processes-typically described in U.S. Pat No. 2, 607,751.

Solution of a fiber forming polymer" relates to those solutions of fiber forming polymer in solvents extruded through the spinnerets in dry and wet spinning processes. Typical solvents for wet and dry spinning are dimethylformamide and dimethylacetamide. Acrylic, spandex, and aromatic polymers are conventionally wet or dry spun. Some acrylic fibers may be spun from solutions containing 25-35 percent polymer. Some spandex fibers may be spun from polymer solutions with concentrations of spandex in the range of 25-40 percent in particular solvents, with concentrations between 15-25 percent.

spinneret-assembly" refers to that part of a wet or dry spinning apparatus which comprises the spinneret and dis 'tribution plates for distributing the solution from the pump across the-cross section of the spinneret so that it is distributed ,in the desired manner to-thespinneret orifices. The spinneret assembly may also contain filter screens. The spinneret assemblymay provide for distribution of different polymer feeds to different part of the spinneret as for the spinning of bicomponent fibers. Thus, the term spinneret assembly as used herein has the meaning usually used in the art. Typical of the spinneret assemblies for use with spinning of fibers from solution include those described in U.S. Pat. Nos. 3,458,616 and 3,509,244.

Spandex polymer as used herein has its typical meaning in the art and refers to'long chain synthetic elastomer comprised of at least 85 percent of a segmented polyurethane among which are solution spun segmented polyurethanes such as described in several patents among which are U.S. Pat Nos.

2,929,801; 2,929,802; 2,929,803; 2,929,804; 2,953,839; 2,957,852; 2,962,470; 2,999,839; and 3,009,901. This process is also applicable to solution spun aromatic polyamides such as those described in U.S. PAT. Nos. 3,094,5l 1; 3,287,324; 3,322,728; 3,349,062; 3,354,125; 3,414,645; and 3,380,969.

The term "acrylonitrile polymer". as used herein, refers to any long chain synthetic polymer composed of at least 85 by weight of acrylonitrile units of the formula,

in the polymer chain. As is well understood, the term includes both the homopolymer of acrylonitrile and copolymers of acrylonitrile and monoethylenically unsaturated monomers polymerizable with acrylonitrile. Non-limitative examples of preferred comonomers include methyl acrylate, methyl methacrylate, vinyl acetate, styrene, methacrylamide, methacrylonitrile, vinyl chloride, vinylidene chloride, methyl vinyl ketone, 2-vinylpyridine, 4-vinylpyridine, 2-methyl-5- vinylpyridine, and sodium styrene sulfonate.

' The gas more soluble than air which replaces the air on the spinneret assembly must not be unduly corrosive to eq uipment, should not be toxic for safety reasons and of course must be inert in thesolution to be spun.

The range of suitable gases will, therefore, vary with the solvent and polymer in the solution to be spun. However, for solutions of acrylic or spandex polymer in dimethylformamide or dimethylacetamide CO is preferred. Nitrogen is less soluble than air in solutions of acrylic polymer or spandex polymer in dimethylformamide and dimethylacetamide, and is not a suitable gas according to this invention for replacement of air in spinneret assembly for spinning fibers from these solutions. Oxygen" is not inert to the solution to be'spun.

DESCRIPTION OF THE DRAWING FIG. 1 shows a typical spinning head for which this invention is useful. Spinning solution from a source not shown is delivered to conduit 1 which passes through heating chamber 3. Heat transfer fluid enters the chamber 3 through passage 5 and exits through passage 7. Spinning solution from conduit 1 flows through the spinneret assembly consisting of pack body 9, filter pack 11, distributor plate 13, spinneret 1S, retainer plate 17, bolt 19, and threaded ring 21 which holds the as sembly in place.

Hot gas from a source not shown is delivered through conduit 23 to gas distributor chamber 25 which is insulated from K the heating chamber as shown and from which it flows through turbulence supressing means consisting of perforated plate 27 and screen 29 to contact the filaments in the spinning cell. The filaments lose the bulk of the solvent to the hot, evaporative solids. Some aromatic polyamides may be spun from solutions, medium as they progress through the spinning cell not shown EXAMPLE I This example illustrates the improved startup performance spinning acrylic fibers. An acrylic spinning cell as shown in US. Pat. No. 3,458,616 is used for this test. This cell uses a spinneret assembly consisting of the upper and lower distribution plates, spinneret plate, ring nut, and cap screw illustrated in that patent and has two solution inlet portsone supplying 930 spinneret orifices arranged in an annular pattern at the periphery of the spinneret and the other supplying 930 orifices arranged in an annular pattern surrounding the center of the spinneret. The assembly is preheated in an oven to 125C. and removed from the preheat oven. A cylinder of commercially available CO with a pressure regulator adjusted to supply gas at 5 psig. is connected through one-fourth ID rubber tubing and a rubber stopper to the inlet port supplying polymer to the holes at the spinneret periphery and this section of the assembly is purged for seconds. The rubber tubing is then connected to the inlet port supplying holes surrounding the spinneret center and this section is purged for 5 seconds. The solution supply port to the inner circle of holes is then plugged with a rubber stopper. CO is again connected to the port supplying the outer periphery and this section is again purged for 10 seconds. The plug and CO supply tubing are removed and the assembly is immediately installed in the spinning cell. The cell is closed and nitrogen gas heated to 357 C. is supplied continuously to the cell. A 32 percent solution by weight of polyacrylonitrile in dimethylformamide is divided into two portions which are then heated separately in apparatus shown in the reference patent. One portion is heated to 122 C. and extruded through the spinneret outer orifices while the second portion is heated to I34 C. and extruded through the spinneret inner orifices. Total polyacrylonitrile supply to the spinning cell is 70 pounds per hour (32 kilograms per hour). Startup of the cell using purged spinneret assembly according to the present invention is characterized by reduction of interrupted filaments and reduced deposits of spinning solution on the spinneret face. Using this purging technique, 49 successful startups are obtained in 56 attempts as compared to 50 successful startups in 82 attempts when no purging is used.

EXAMPLE II This example demonstrates the improved startablility resulting from using the purging technique of this invention in spinning spandex fibers. The spinning cell and process described in example 1 of US. Pat. No. 3,271,818 is used in these tests with the exception that nitrogen gas heated to 415 C. is used as the evaporative medium instead of Kemp gas heated to 300 C. and the gas deflecting band is omitted.

A cylinder of commercially available CO gas with a pressure regulator set to supply gas at 4 psig. is connected through rubber tubing to a cap which fits over the spinning assembly. The cap is mounted on the spinning assembly and CO is purged through the assembly for 2 minutes. The assembly is immediately mounted in the spinning cell. Startup is characterized by absence of deposits of polymer on the spinneret face and absence of broken filaments as well as marked reduction in the number of reduced denier filaments resulting from spinning solution deposit around the individual spinneret capillaries. Using this purging technique, 15 such uninterrupted spinneret startups are accomplished in 15 such uninterrupted spinneret startups are accomplished in IS attempts. In contrast, without purging with CO 20 startups yield only 13 successful startups 7 false starts requiring replacement of the spinneret assembly.

What is claimed is:

1. In a process for dry spinning textile filaments from a spinning solution of a fiber forming polymer in a solvent selected from the group consisting of dimethylformamide and drmethylacetamide comprising forcing said solution through a spinneret assembly; the improvement comprising removing air from said spinneret assembly, before passing solution therethrough during spinning, by replacement of said air with carbon dioxide gas, said gas being more soluble than said air in the spinning solution.

2. The process of claim 1 wherein the fiber forming polymer comprises acrylonitrile polymer.

3. The process of claim 1 wherein the fiber forming polymer comprises spandex polymer.

4. The process of claim 1 wherein the fiber forming polymer comprises aromatic polyamide. 

2. The process of claim 1 wherein the fiber forming polymer comprises acrylonitrile polymer.
 3. The process of claim 1 wherein the fiber forming polymer comprises spandex polymer.
 4. The process of claim 1 wherein the fiber forming polymer comprises aromatic polyamide. 